We report here on a case of mucinous adenocarcinoma that probably originated in the renal pelvis of a horseshoe kidney. A 61-year-old woman presented with a palpable mass in the left upper quadrant of the abdomen, and this mass had been present for several months. Computed tomography (CT) revealed a left renal pelvic tumor in the horseshoe kidney. Grossly, a 10×9×8 cm unilocular cystic mass fil...